This invention relates to a silicon nitride type composite ceramic material reinforced with use of silicon carbide whiskers. More particularly, it is concerned with a composite ceramic material which is widely useful as a material for cutting tools capable of performing high speed cutting of high nickel, cast ion, steel, aluminum, titanium, and generally those materials having difficulty in cutting, or structural members or parts for automobile engines such as ceramic valves, etc., or other members required to have wear-resistance, corrosion-resistance and heat-resistance.
The silicon nitride (Si.sub.3 N.sub.4) type ceramic contaning silicon nitride as the principal component is excellent in its mechanical strength, oxidation-resistance, wear-resistance, thermal-shock-resistance, corrosion-resistance, and others. Thus there has already started practical use thereof as structural materials for the engines and materials for the cutting tools.
However, in spite of such excellent characteristics, it is poor in its qualitative stability and homogenity, when compared with those of metals, hence much higher toughness has been desired of the silicon nitride ceramics from the standpoint of improvements in its working reliability as well as high mechanical properties. For this purpose, there have been made many attempts to produce composite bodies of silicon nitride ceramics, in which silicon carbide (SiC) whisker is sued as the reinforcing material, as disclosed in Japanese Patent Kokoku-Publication Nos., 58-51911, 60-35316, and 60-55469; Japanese Patent Kokai-Publication Nos. 59-102862, 60-200863, 60-246268, 61-291463, and so forth. Even these attempts, however, have not yet reached their level of sufficient practicability, and there is much to be desired in improvement in its toughness.
In addition, the composite material of silicon nitride which exhibits difficulty in its sintering property, because of the anisotropy of SiC whiskers, could be obtained only by the pressure sintering, but could not be obtained by the normal pressure sintering and the gas pressure sintering (in a pressurized gas atmosphere at 10 atms. or below). Thus the productivity upon manufacturing such composite materials has not been satisfactory.